A mobile telephone is normally supplied from a battery incorporated in a housing which may be separate from the hand module of the mobile, or alternatively capable of being inserted thereonto. It is also possible to supply the mobile from a conventional vehicle battery, wherewith the mobile is connected, for example, to the cigarette lighter terminal by means of a separate cable. It is only possible to supply power to the mobile from the cigarette lighter terminal when the voltage of the vehicle battery lies between the maximum and minimum permitted operating voltages.